The present invention relates generally to a valve assembly having valve actuators and, more particularly, to valve actuators which provide for both rotational and axial translational movements of a valve stem. Yet more particularly, the invention relates to a valve for use in aggressive applications, such as alumina production facilities, which includes self-cleaning means toward assuring proper fit and seal between the valve gate and its corresponding seat.
In many applications it is desirable to have the ability to move the stem of a valve in two manners, axially and rotationally. For example, in some industrial applications it is desirable when closing the valve to first move the valve stem axially so that the valve gate contacts the valve seat and then to rotate the valve stem so the valve gate grinds against the seat to remove any buildup of deposited material which may have otherwise acted to prevented a complete closing of the valve.
Valves for use in aluminum manufacturing facilities have been particularly subject to bauxite buildup between the valve gate and valve seat. Generally speaking these valves have an elbow-shaped construction, in such a manner that the valve gate is extended on a shaft which traverses the valve body and is terminated in a spindle having a complementary threaded nut element, so that said threaded nut element, through whatever means of conventional operation, provides the spindle with the necessary axial motion for carrying out valve opening/closing.
Conventionally the periodical cleaning of such valves has been carried out by hand, after valve dismantlement, which clearly involves an interruption in the process of producing alumina, with the consequent repercussion that this implies.
Publication WO 99/61829 purportedly discloses a valve seat self-cleaning device having a blocking collar capable of being manually coupled to and decoupled from the valve assembly. Through said collar and with the valve in a shut position, the nut and the spindle could be blocked, with an accompanying release of the spindle in the angular sense so that the rotary movement applied to the nut, instead of being converted into an axial displacement of the spindle, was directly transmitted to said spindle. As a result the gate, instead of being retracted with respect to the valve seat, is rotated with respect to the latter producing a friction effect and the consequent elimination of bauxite deposits or scale, i.e. a valve self-cleaning effect was obtained, without the need to proceed to the dismantling of the valve body. However this valve assembly in addition to requiring a manual intervention for the coupling/decoupling of the blocking collar, meant that in a situation of keying of the nut to the spindle (that is, in the cleaning phase), the spindle could not be advanced. As a result, the duration of the cleaning operation became longer as the depth of the scale became deeper, since after a first friction application, in which the surface layer of the scale was removed, the friction effect between gate and seat likewise disappeared, it being necessary to dismantle the blocking collar, re-adjust the gate to the seat and re-couple the blocking collar. In some instances it even being necessary for the operation to be repeated several times, depending on the depth of the scaling.
The present invention provides a multiple mode valve actuator structure for controlling the operation of a valve and providing for axial and/or rotational movement of the valve gate relative to the valve seat. In one embodiement, the valve includes a partially threaded valve stem spindle engaging a threaded nut element to provide for axial movement of the valve stem. The apparatus includes a first drive motor which is activated during the first mode of valve actuator operation (axial movement). A first crown gear drive assembly operatively couples the first drive motor to the valve stem via an intermediate spindle. A second drive motor, which is activated during the second mode of valve actuator operation (rotational movement) is operatively coupled to the valve stem via a second crown gear drive assembly and stem engagement structure. During the first mode of valve actuator operation, the valve stem is axially driven by the first gear drive assembly, through a threaded nut element engaging a threaded valve stem spindle. During a second mode of operation, both gear drive assemblies are driven to both rotate and axially transition the valve stem. A control device may be provided to control the mode of operation the valve actuator. The first and second drive motors may be driven in multiple modes separately for independent axial or rotational movement of the stem, or simultaneously for axial and rotational movement of the stem.
A particular valve according to the present invention for alumina production plants is based on the principle of self-cleaning through friction, by rotation of the gate against the valve seat permitting complete automation of the cleaning process.
To this end, in a more specific way and based on a conventional valve body with its pertinent valve seat and gate, the latter in association with a shaft capable of undergoing a movement of axial displacement by means of a spindle-nut mechanism, the valve of the invention centers its characteristics on the fact that in said spindle two coaxial sectors are established, one constituting the spindle itself, axially displaceable with the collaboration of the corresponding and aforesaid nut, and another constituting the gate supporting shaft, with the particularity that these two elements, shaft and spindle, are inter-coupled with the assistance of a sleeve which, immobilising one with respect to the other in the axial sense, permits however the free rotation of the shaft with respect to the spindle.
Complementing the structure described the sleeve mentioned is conveniently keyed to another external sleeve, through which the internal sleeve and consequently the shaft to which the gate is joined and the gate itself, can undergo a rotation without the latter affecting the spindle, whereby the latter can turn freely with respect to the shaft.
However, a key that couples the two sleeves mentioned lies in a groove in one of the sleeves, preferentially the internal sleeve, of sufficient length to permit the relative axial movement between the two sleeves corresponding to the change from one of the limiting positions to the other of the gate with respect to the valve seat.
In accordance with another of the characteristics of the invention, both the nut corresponding to the spindle, and the external sleeve that transmits the rotary movement to the gate, each have a toothed crown gear, said gears being operable by means of bevel pinions, through respective reduction gear motors, electrical or hydraulic, in such a manner that the operation of one of them shall produce the valve opening-shutting action, and the operating of the other shall produce the rotary movement of the gate with respect to its seat, it being clear that both motors can work simultaneously, in such a manner that in the cleaning phase and as the scale is progressively removed by friction from the gate and from the valve seat, said gate shall gradually progress towards the seat, in order that this self-cleaning phase does not lose its efficacy.